Glass frit

Abstract

A glass frit is prepared by heating an initial glass frit in the presence of a reducing agent so as to reduce metal moiety in the glass structure of the frit and then cooling the reaction mixture. Preferably, the frit prepared is used in a method of forming electrically conducting silver tracks on enamel on glass windows, by applying to window glass an enamel composition containing the frit and on top thereof a silver composition in the shape of the tracks and firing the compositions, such that on the firing the reduced metal moiety reduces silver ions migrating through the enamel composition from the silver composition to elemental silver and thereby prevents or impairs them from interacting with the glass to form visible tracks.

What is claimed is: 
     
       1. process for preparing a glass frit adapted to be applied to a glass member (c) and also adapted to have a metallic element (a) deposited thereon wherein, upon firing of said frit, together with said metallic element and said glass member, said frit prevents migration of metallic ions from (a) to (c), which process comprises heating an initial glass frit in the presence of a reducing agent so as to reduce at least one metal moiety ion in the glass structure of said frit and then cooling said frit for subsequent deposition on said glass member, and for receiving said metallic element thereon. 
     
     
       2. A process for preparing a glass frit suitable for use in enamel compositions for preventing or impairing the migration of silver ions through the enamel composition on firing, adapted to be applied to a glass member (c) and also adapted to have a metallic element (a) deposited thereon wherein, upon firing of said frit, together with said metallic element and said glass member, said frit prevents migration of metallic ions from (a) to (c) which process comprises heating an initial glass frit in the presence of a reducing agent so as to reduce at least one metal moiety of the glass structure of the frit and then cooling the frit, the reduced metal moiety being capable of reducing, to elemental silver, silver ions migrating through the enamel composition on firing. 
     
     
       3. A process according to claim 1, wherein the reducing agent is solid. 
     
     
       4. A process according to claim 3, wherein the reducing agent is sucrose. 
     
     
       5. A process according to claim 1, wherein the reduction is performed at a temperature below the softening point of the initial frit. 
     
     
       6. A process according to claim 1, wherein the reduction is carried out in the presence of pigment. 
     
     
       7. A process according to claim 6, wherein the pigment is black pigment free from copper moieties. 
     
     
       8. A process according to claim 1, wherein the glass frit prepared is free from sulphur moieties. 
     
     
       9. A glass frit prepared by the process of claim 1. 
     
     
       10. A glass frit prepared by the process of claim 2. 
     
     
       11. A frit according to claim 9, wherein the metal is bismuth. 
     
     
       12. A frit according to claim 9, which contains at least 1% by weight of the reduced metal moiety. 
     
     
       13. An enamel composition for glass, which composition comprises pigment and a glass frit claimed in claim 9. 
     
     
       14. An enamel composition for glass windows, which composition is for obscuring, from view through the glass window, electrically conducting silver tracks formed on the enamel on the other side of the glass, the composition comprising pigment and a glass frit which has been prepared by a process claimed in claim 2. 
     
     
       15. A composition according to claim 13, wherein the pigment is black pigment. 
     
     
       16. An enamel composition for glass windows, which composition is for obscuring, from view through the glass window, electrically conducting silver tracks formed on the enamel on the other side of the glass, the composition comprising pigment and a glass frit which has been prepared by a process claimed in claim 6 and the pigment in the composition comprises that employed in the process. 
     
     
       17. A method of forming enamel on glass by applying to glass an enamel composition and firing the composition, wherein the enamel composition is as claimed in claim 13. 
     
     
       18. A method of forming electrically conducting silver tracks on enamel on glass windows, by applying to window glass an enamel composition and on top thereof a silver composition in the shape of said silver tracks and firing said enamel and said silver compositions, in which method the enamel composition is as claimed in claim 14, such that on firing, at least one metal moiety of said enamel composition reduces silver ions migrating through the enamel composition from said silver composition to elemental silver and thereby prevents or impairs them from interacting with the glass to form visible tracks.